The present invention concerns methods and apparatus involving the measurement of characteristics of a small quantity of fluid dropped into the little measuring dish or measuring pan of a dish transducer unit. The small quantity of fluid is dropped into the little dish of the transducer unit, and directly contacts the transducer of the unit immediately, or flows down the side of the little dish to the center of the dish, where it then makes physical contact with the transducer of the transducer unit. Such dish transducer units are thermostatically heated, both the transducer unit itself and the little dish or pan thereof, for operativeness and in order to bring the small quantity of fluid up to requisite temperature before actually performing the measurement for which the transducer is employed. One known transducer unit of this type employs a polarographic oxygen-concentration transducer and a drop of blood is dropped into the little dish of the transducer for a polarographic blood-oxygen concentration measurement. However, such dish transducer units are also employed to measure other properties and of other fluids.
Such dish transducer units are often portable and provided with their own battery. In that case, the factor of energy consumption becomes a significant problem, because considerable amounts of energy are required to bring the transducer of the unit and the dish of the unit up to operative temperature. Accordingly, after the transducer unit's thermostatic system has brought the transducer up to operative temperature, and thereafter continues to keep the transducer at operative temperature, delay in actual performance of the measurement involved can be very wasteful of energization. In order to minimize energy waste, the measurement should ideally be performed as soon as possible after the operative temperature has been reached. On the other hand, because the heating power of the transducer unit's battery may be rather low, a considerable length of time, e.g., more than a minute, may be required for the warm-up operation. If the user, because he becomes impatient from the desire to avoid heating-energy waste, or for other reasons, performs the measurement before the warm-up period is through, the result of the measurement may be highly inaccurate. Thus, these two factors tend to a certain extent, to contradict each other.
Furthermore, usually the drop of fluid placed into the little dish must itself be brought up to a certain temperature, before performing the measurement. This involves further delay before the measurement can be properly performed, and likewise if this heating, which is likewise thermostatically performed, is continued too long, heating-energy waste once more ensues.
These two problems, the time required to warm up the transducer and the time required to warm up the drop of fluid to be measured, are of identical character, but they represent two sources of difficulty, not one. Thus, for example, it is in general not appropriate merely to drop the drop of fluid into the dish of the transducer at the start of the warm-up of the transducer unit's transducer, i.e., in order to combine the two warm-up operations with respect to time. Instead, it is generally necessary first to bring the transducer up to operative temperature, before dropping in the drops of blood or the like, so that the meter of which the transducer unit forms a part can be adjusted or calibrated prior to the actual measurement. I.e., only after the transducer has been brought to operative temperature, and then the meter adjusted or calibrated, is the drop of blood, or the like, to be dropped in, and then the second warm-up period commences. With dish-type transducer units, e.g., incorporating a polarographic oxygen-concentration transducer, the meter involved may be very sensitive even to changes of ordinary atmospheric pressure, so that such readjustment or calibration may be necessary very often. For the same reason, after the first warm-up period and the subsequent adjustment or calibration is performed, the drop of blood or the like should be dropped in as soon as possible and the measurement performed, i.e., before the calibration can begin to grow stale.